Mysql – Are these custom module Drupal tables lacking foreign keys? thesqldump with table structures without data is included

I am troubleshooting a some tables in MySQL used by a custom Drupal module. Documentation for these tables is poor so I used mysqldump to get the structures in the Drupal database without the data. I know nothing really about InnoDB but have been doing regular MySQL database stuff for a while now.

In the below examples there should be a table named corporate_subscription_flag_list with

• A Primary Key: subscription_id
• A Foreign Key: sflid

mysqldump shows a table named `corporate_subscription_flag_list, like:

DROP TABLE IF EXISTS 'corporate_subscription_flag_list';
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE 'corporate_subscription_flag_list' (
    'sflid' int(10) unsigned NOT NULL AUTO_INCREMENT
    'subscription_id' int(11) NOT NULL
    'subscription_flag_id' int(11) NOT NULL
    PRIMARY KEY ('subscription_id')
    KEY 'sflid' ('sflid')
) ENGINE=InnoDB AUTO_INCREMENT=75 DEFAULT CHARSET=utf8;
/*!40101 SET character_set_client = @saved_cs_client */;

However sflid only exists in the above table – am I wrong, or is the way it's been done wrong? sflid isn't a primary key in any other table nor is it a column in any other table in the database.

Looking at the other tables that supposedly use subscription_id as a foreign key to reference corporate_subscription_flag_list it seems, to me, that there is also a problem.

Comments seem to suggest (as does a strange diagram I have found) that corporate_promolist_data (another table) uses subscription_id as a foreign key referencing corporate_subscription_flag_list.

However, unless I'm missing something there is no foreign key being defined, unless KEY 'pludid' ('pludid') is defining a foreign key?

DROP TABLE IF EXISTS 'corporate_promolist_user_data';
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE 'corporate_promolist_user_data' (
    'pludid' int(10) unsigned NOT NULL AUTO_INCREMENT
    'subscription_id' int(11) NOT NULL
    'title' varchar(255) DEFAULT NULL 
    'first_name' varchar(255) DEFAULT NULL
    'last_name' varchar(255) DEFAULT NULL
    'email_address' varchar(255) DEFAULT NULL
    'organisation' varchar(255) DEFAULT NULL
    'job_title' varchar(255) DEFAULT NULL
    'department' varchar(255) DEFAULT NULL
    'address_line_1' varchar(255) DEFAULT NULL
    'address_line_2' varchar(255) DEFAULT NULL
    'town_city' varchar(255) DEFAULT NULL
    'county_state' varchar(255) DEFAULT NULL
    'post_code' varchar(255) DEFAULT NULL
    'country_id' varchar(255) DEFAULT NULL
    PRIMARY KEY ('pludid')
    KEY 'pludid' ('pludid')
) ENGINE=InnoDB AUTO_INCREMENT=22 DEFAULT CHARSET=utf8;
/*!40101 SET character_set_client = @saved_cs_client */;